1 Sports-Related Head Injury

Minh Quan Le, Mohammed Emam, Alexis M. Coslick, and Daniel Krasna

1.1 Traumatic Brain Injury Overview

1.1.1 Classification

Traumatic brain injury (TBI) is defined as an “alteration in brain function, or other evidence of brain pathology, caused by an external force.” ▶ [1] Clinically, TBI severity is often based on the Glasgow Coma Scale (GCS). Mild injuries make up the overwhelming majority of sports-related injuries both in the general population engaging in recreational sports and professional athletes. ▶ [2] There are numerous scales to classify severity of brain injury, many of which incorporate some combination of the GCS level, duration of post-traumatic amnesia (PTA), duration of loss of consciousness (LOC), alteration of consciousness (AOC), and focal neurologic deficits. ▶ [3],​ ▶ [4],​ ▶ [5] Based on these scales, patients can be classified as having mild, moderate, or severe brain injury ( ▶ Table 1.1  ). Given the inconsistency of accurate reporting for both PTA and LOC, GCS scores are most commonly used clinically for assessing severity. ▶ [6] However, it is important to recognize that GCS alone provides insufficient information for capturing both extremes of severity and does not correlate well to outcomes. ▶ [7],​ ▶ [8] Even with additional demographic information and examination findings, the accuracy of predicting outcomes is below 40%. ▶ [6]

The diagnostic criteria for mild TBI vary among different guidelines. ▶ [5],​ ▶ [9],​ ▶ [10] Within the world of sports, mild TBI is often used interchangeably with concussion. The consensus statement from the international Concussion in Sport Group (CISG) defines sports-related concussion (SRC) as an alteration of brain function caused by an external force that usually has “rapid onset of short-lived impairment of neurological function that resolves spontaneously,” though signs and symptoms may “evolve over a number of minutes to hours.” LOC is not required but possible. ▶ [11]

1.1.2 Epidemiology

Global estimates of TBI show an annual incidence of 69 million of which over 80% are mild. ▶ [12] Sports and recreational activities may be responsible for over 1.6 million TBIs with a similar predominance of mild injuries. ▶ [2] Severe brain injuries in sport are more often related to cycling and equestrian sports. In both groups, more severe injuries are seen in unhelmeted riders. ▶ [13] A study by Winkler et al further illustrates the importance of proper helmet use. They noted that winter board sports such as skiing and snowboarding where helmet use is high had lower mortality than roller sports such as skateboarding where helmet use is very low. ▶ [14]

Given that the majority of TBIs in sports are mild, databases have been set up looking at SRC across various sports associations. During the National Collegiate Athletic Association (NCAA) seasons 2014/15 to 2018/19, there were 4.13 mild TBIs per 10,000 athlete-exposures (AEs) reported for 23 sports, showing a decrease from 4.47 per 10,000 AEs in 2009/10 to 2013/14 reported for 25 sports. ▶ [15],​ ▶ [16] Across both men’s and women’s collegiate sports, men’s ice hockey had the highest rate of SRC at approximately 7.35 per 10,000 AEs, followed by women’s soccer with 7.15 per 10,000 AEs. Men’s track and field had 0.33 per 10,000 AEs and women’s track and field reported 0.17 in 1,000 AEs. ▶ [15] An analysis of high school sports during the 2013/14 to 2017/18 school years found 4.17 concussions per 10,000 AEs across 20 sports. ▶ [17] American football had the most reported concussion at 10.40 per 10,000 AEs and girls’ soccer registered 8.19 per 10,000 AEs. ▶ [17]

The highest reported mechanism of injury was player contact, which accounted for approximately 85.1% of concussions in collegiate men’s American football and 83.8% in men’s basketball. ▶ [15] Most SRC in women’s sports was attributed to equipment/apparatus contact in collegiate and high school sports, although collegiate women’s ice hockey (45.9%), women’s soccer (42.5%), and women’s basketball (64.1%) had a greater incidence of player contact. ▶ [15] Across both sexes, and disciplines, the majority of SRC occurred during competition, with 54.5% of concussions happening in the second half or third or fourth quarter. ▶ [15],​ ▶ [17],​ ▶ [18]

Partitioning for sex, there was a higher incidence of SRC in collegiate soccer, basketball, and softball/baseball in women relative to men. ▶ [15],​ ▶ [19] A similar trend was demonstrated in high school, with higher SRCs in girls than boys at 3.35 versus 1.51 per 10,000 AEs, respectively. High school boys and collegiate men’s ice hockey had the highest prevalence of recurrent concussion at 14.4 and 10.6%, respectively. ▶ [15],​ ▶ [17]

1.1.3 Pathophysiology

Injuries to the brain can be described both by timing as well as by location. Patients can have injuries focally at the site of impact as well as diffusely due to global force from acceleration and deceleration. Examples of focal injuries include skull fractures, contusions, and hemorrhage. ▶ [20] Focal injuries cause specific functional deficits depending on laterality and lobe. The structure of the skull puts the temporal and frontal lobes at higher risk of injury. Damage to these areas is responsible for the neurobehavioral profile often associated with more severe TBI. ▶ [21]

Diffuse injuries include axonal injury. The different tissue densities within the brain makes the axons in white matter particularly susceptible to damage from rotational acceleration. Damage initially affects the axon membranes at nodes of Ranvier, causing disruption of ion transport, subsequent swelling, and potential retraction of the axon. More severe injuries can cause structural damage. Given the role of axons in connecting various regions of the brain, diffuse axonal injury (DAI) can cause a wide range of impairments, and the severity of DAI correlates with the duration of LOC. ▶ [22]

Diffuse and focal injuries present at the time of impact are referred to as primary injury and these trigger cascades in the following minutes to days causing secondary injury. ▶ [20] TBI initially causes disruption of cell membranes leading to glutamate and potassium release as well as accumulation of intracellular calcium. This is followed by energy consumption and a drop in glucose levels. The degree of ionic disruption and glucose depletion correlates with injury severity. ▶ [23] These changes...